lrepeat was defined in TIP 136 [http://www.tcl.tk/cgi-bin/tct/tip/136.html] , 
which has been approved for incorporation into Tcl 8.5.0 .

Eventually, the doc will be here:
http://www.tcl.tk/man/tcl8.5/TclCmd/lrepeat.htm

 lrepeat number element1 ?element2 element3 ...?

This command builds up a list by repeating elements.  It will be a part of
Tcl 8.5.0 .  Note that Tcl 8.5 is available in an early developer form from ftp://ftp.tcl.tk/pub/tcl/nightly-cvs/tcl-*gz .  Early access to Tk 8.5 is there as well.

An example of how it will work is

 lrepeat 3 a => a a a
 lrepeat 3 [lrepeat 3 0] => {0 0 0} {0 0 0} {0 0 0}
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[RS]: Note the possible confusion with [string repeat]'s syntax:
 % string repeat a 5
 aaaaa

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[FW]: A forward-compatible version for versions before 8.5 is available in [Additional list functions]
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[LES] How is '''[[lrepeat 3 a]]''' different from '''[[string repeat "a " 3]]'''? 

And how is '''lrepeat 3 [[lrepeat 3 0]]''' different from '''string repeat [[list [[string repeat "0 " 3]]]] 3'''?

[RS] The first creates a list, while the second creates a string that can be parsed into a list. For short lists, this doesn't matter much, but I noticed extra time costs of about half a second when converting a 2000x2500 list-like string to a nested list.

[LES] Half a second? In the entire operation or each nested list? Mentioning once again that I am completely ignorant of C, I wonder if it wouldn't have been possible to rewrite [string repeat] and optimize it, using whatever method '''lrepeat''' uses to do its trick. This '''lrepeat''' command still strikes me as something a bit superfluous. I mean, something rather more suitable to the [Bag of algorithms] than the core.

[LES] Does anyone realize that one requires '''number - string''' while the other requires '''string - number''', and that is an excellent method to prevent people from memorizing correct syntax? - [RS] pointed this out just 11 lines above :^)  [LES] I thought you were just pointing out that one adds spaces in-between (list) and the other concatenates it all together (string).
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[Category Command]